Add WebThread in AudioDestination to support AudioWorkletThread

third_party/WebKit/Source/platform/audio/PushPullFIFO.h

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef PushPullFIFO_h
 #define PushPullFIFO_h
 
 #include "platform/audio/AudioBus.h"
 #include "platform/wtf/Allocator.h"
+#include "platform/wtf/Functional.h"
+#include "platform/wtf/Threading.h"
+#include "platform/wtf/ThreadingPrimitives.h"
 #include "public/platform/WebCommon.h"
 
 namespace blink {
 
 // A configuration data container for PushPullFIFO unit test.
 struct PushPullFIFOStateForTest {
   const size_t fifo_length;
   const unsigned number_of_channels;
   const size_t frames_available;
   const size_t index_read;
   const size_t index_write;
   const unsigned overflow_count;
   const unsigned underflow_count;
 };
 
 // PushPullFIFO class is an intermediate audio sample storage between
 // Blink-WebAudio and the renderer. The renderer's hardware callback buffer size
 // varies on the platform, but the WebAudio always renders 128 frames (render
 // quantum, RQ) thus FIFO is needed to handle the general case.
+//
+// Note that this object is concurrently accessed by two threads; WebAudio
+// rendering thread (WebThread) in Blink and the audio device thread
+// (AudioDeviceThread) from the media renderer. The push/pull operations touch
+// most of variables in the class (index_write_, index_read_, frames_available_,
+// and fifo_Bus_) so the thread safety must be handled with care.
+//
+// TODO(hongchan): add a unit test for multi-thread access.
 class BLINK_PLATFORM_EXPORT PushPullFIFO {
   USING_FAST_MALLOC(PushPullFIFO);
   WTF_MAKE_NONCOPYABLE(PushPullFIFO);
 
  public:
   // Maximum FIFO length. (512 render quanta)
   static const size_t kMaxFIFOLength;
 
   // |fifoLength| cannot exceed |kMaxFIFOLength|. Otherwise it crashes.
   explicit PushPullFIFO(unsigned number_of_channels, size_t fifo_length);
   ~PushPullFIFO();
 
   // Pushes the rendered frames by WebAudio engine.
   //  - The |inputBus| length is 128 frames (1 render quantum), fixed.
   //  - In case of overflow (FIFO full while push), the existing frames in FIFO
   //    will be overwritten and |indexRead| will be forcibly moved to
   //    |indexWrite| to avoid reading overwritten frames.
   void Push(const AudioBus* input_bus);
 
   // Pulling |framesRequested| by the audio device thread.
   //  - If |framesRequested| is bigger than the length of |outputBus|, it
   //    violates SECURITY_CHECK().
   //  - If |framesRequested| is bigger than FIFO length, it violates
   //    SECURITY_CHECK().
   //  - In case of underflow (FIFO empty while pull), the remaining space in the
   //    requested output bus will be filled with silence. Thus it will fulfill
   //    the request from the consumer without causing error, but with a glitch.
-  void Pull(AudioBus* output_bus, size_t frames_requested);
+  void Pull(AudioBus* output_bus,
+            size_t frames_requested,
+            std::unique_ptr<WTF::Function<void(size_t, size_t)>>
+                push_request_render_callback);

[hongchan, 2017/04/14 16:31:48]

@nhiroki @haraken Let me know if this is a weird thing to do in Blink.

 
-  size_t FramesAvailable() const { return frames_available_; }
   size_t length() const { return fifo_length_; }
   unsigned NumberOfChannels() const { return fifo_bus_->NumberOfChannels(); }
-  AudioBus* Bus() const { return fifo_bus_.Get(); }
+
+  // TODO(hongchan): This is unsafe even for testing. Consider refactoring.
+  AudioBus* GetFIFOBusForTest() const { return fifo_bus_.Get(); }
 
   // For unit test. Get the current configuration that consists of FIFO length,
   // number of channels, read/write index position and under/overflow count.
   const PushPullFIFOStateForTest GetStateForTest() const;
 
  private:
   // The size of the FIFO.
   const size_t fifo_length_ = 0;
 
   RefPtr<AudioBus> fifo_bus_;
 
   // The number of frames in the FIFO actually available for pulling.
   size_t frames_available_;
 
   size_t index_read_;
   size_t index_write_;
 
   unsigned overflow_count_;
   unsigned underflow_count_;
+
+  // This lock protects: |fifo_bus_|, |frames_available_|, |index_read_| and
+  // |index_write_|.
+  mutable Mutex lock_;
 };
 
 }  // namespace blink
 
 #endif  // PushPullFIFO_h